LR light reaction (light dependent) reduction reaction
light, water and chlorophyll –> ATP + NADPH + O2
light energy converted to chemical energy in the form of ATP (NADPH is the reducing power to cause reduction)
6H2O + 6CO2 –> C6H12O6 + 6O2
H2O –> H+ + e + O
occurs in membrane of thylakoid
epidermis: transparent, no chlorophyll, light can pass through
guard cells embedded within epidermis
mesophyll (inside cells): two layers of cells –> all have chloroplasts, chlorophyll, can absorb light
top layer (rectangular cells): palisade mesophyll. compact, longer axis of palisade mesophyll at right angle to upper epidermis so that more cells are exposed to sunlight. everyone of them has chlorophyll
bottom layer (circular cells): spongy mesophyll
thylakoid
so many membranes increase surface area to volume ratio
chloroplasts have their own nuclei
electrons get excited, shoot out of chlorophyll
leaves have water coming in from the xylem, carbon dioxide from the stoma
chloroplasts made up of many membranes
outer membrane, inner membrane, thylakoid, granum (stack of thylakoids)
membrane of thylakoid made up of phospholipids
proteins: photosystem 1 (PS1): first discovered. P700: best wavelength of light absorbed in reaction centre
photosystem 2 (PS2): discovered later. P680.
Lumen: centre of thylakoid space
enzymes split water molecule
membrane not permeable to hydrogen, hydrogen ions remain in lumen while oxygen is liberated
electron becomes from oxidised state to reduced state (a lot of energy at this stage)
hydrogen ions concentrated, moves out of lumen through carrier proteins, hence producing ATP
NADPH and ATP (in stoma) are the end products, which go on to power the dark reactions
Hydrogen bond
soil water diffuse by osmosis, enters root hairs to enter the xylem in the roots, part of the vascular bundle, travels up stem into leaves
high pressure of water entering stem, xylem (vessel) is like a drinking straw, suction is evaporation through the vessel, transpiration pull, continuous column of water, water also joined to the wall of the vessel
(forces) cohesion + adhesion (water molecule to wall) –> capillary action for transport
because of two factors: continuous column (cut the stem under water so as not to break the column of water to maintain strong suction of water)
aphids suck plant sap
Autotrophic Nutrition – plant cells structure and adaptation
Autotrophs able to synthesise own food – producers
heterotrophs: unable to synthesise own food, get energy from autotrophs – herbivore, omnivore, carnivore
stomata: - makes sugar too, increase osmotic concentration so water can pass through
- takes in air, carbon dioxide used for photosynthesis
- water leaves the cell as water potential is higher inside
- they are on the underside of the leaves to avoid direct sunlight
- guard cells have chloroplasts, can make food, so osmotic concentration/pressure increases and water potential decreases –> water moves into guard cells from epidermal cells which have higher water potential (they do not contain chlorophyll) –> guard cells become turgid; cell wall on the outer side is thinner so stretches more –> hence the guard cells open
- only open when photosynthesising
Plant Pigments
Main pigment: chlorophyll: a, b. absorb blue and red, reflect green
carotenoids: carotene, xanthophyll. absorb blue and green, reflect mostly yellow
phycocyanin: absorb green and yellow, reflect yellow, orange or red
chlorophyll b, carotene and xanthophyll are accessory pigments; chlorophyll a is the main pigment
light comes in a packet: photon – light shines on pigment, vibrates, energy passed on, excite electrons, until energy accumulated in reaction centre, have enough energy to leave orbit, so electron shoots off from reaction centre and is caught by electron transport chain
electron transport chain (ETC): plastoquinons, b6f complex, ferridoxine, plastocyanin
electron from PS2 moves to PS1. as the electron is transported along the ETC, ATP is synthesised. PS2 –> PS1 –> ATP. the lack of 1 electron in PS2 is replaced by the H+ ions from the water sucked up by the plant, H+ ions goes into the lumen.
electron shoots out at both PS2 and PS1
PS2 –e–> PS1 –e–> NADPH
ATP ATP
therefore, product of light reaction is ATP and NADPH
The light reaction involves two sets of pigments: PS2 and PS1. PS2 is responsible for synthesis of ATP and for the photolysis of water into H+ + e + O2-; PS1 synthesises compound NADPH, the reducing power to reduce carbon dioxide to form ATP
The Calvin's Cycle
Light independent reactions (DR)
carbon dioxide + NADPH –> sugar
takes place in the stroma (semi-liquid substance)
RuBP: Ribulose Biphosphate: molecule that will take in carbon dioxide, made up of 5 carbon joined in a row
5 carbon + 1 carbon from CO2 –> 6C –> split into two: 3C (triose phosphate: glycerate). at this stage, take in ATP and NADPH. ATP –> ADP (–> AMP); NADPH <–> NADP+ + H+. One 3C will need 2ATP and 1NADPH to form 3C glyceraldehyde –> product: glucose –> entry of ATP and ADP –> remainder goes back to RuBP: CYCLE
1 of the 3C forms glucose while the other 5 goes back to RuBP
Big picture:
convert solar energy to chemical energy
second step is independent, solar energy already captured, needs carbon dioxide for carbon fixation, using the chemical energy from ATP
Structure
Function
Leaf: thin, flat
Maximises surface area to volume ratio for photosynthesis; gases can pass easily, have excess to upper mesophyll layer
Waxy cuticle
Prevents water loss through transpiration; focuses sunlight like a convex lens
Epidermis: transparent (no chlorophyll) & thin
Allows sunlight to reach mesophyll tissue for photosynthesis; protects internal tissues from mechanical damage
Palisade mesophyll:thin-walled cells with cylindrical shape, packed with chlorophyll, orientated vertically and compactly along upper epidermis
Maximises number of cells that are exposed to sunlight for maximum photosynthesis
Spongy mesophyll: round-shaped cells are arranged in loose and open arrangement (large intercellular air space), contain fewer chloroplasts, found nearer lower epidermis
Allows carbon dioxide to diffuse; interchange of gases; nearer to stoma
Stomata: on the underside of leaf, pair of bean-shaped guard cells which contain chloroplasts, outer wall is thin while inner wall is thin, size regulated by guard cells
Prevents excess water loss through transpiration; photosynthesises to open guard cells; outer wall stretches more when cell is turgid to allow opening of stomata
Leaf vein system-vascular bundle: xylem cells situated towards upper epidermis while phloem cells situated towards lower epidermis
Transports water to mesophyll tissue for photosynthesis as well as transports glucose/sucrose away to other parts of the plant (as too much glucose will overly increase the osmotic concentration of the cells); provides support which keeps the leaf up
Chloroplast: many membranes
Increases surface area to volume ratio
starch: storage substance – insoluble, immobile, inert
destarching: plant kept in darkness for few days
1) put leaf in water – kills the enzymes to stop reaction
2) put leaf in ethanol to decolourise leaf so that colour change can be observed –> ethanol dissolves the lipids in the cell membrane so chlorophyll leaks out
Factors affecting photosynthesis Carbon dioxide
Light
Temperature: with every 10 degree Celsius increase in temperature, photosynthesis rate doubles
- enzymes: water molecules bind to enzymes to split
- on hot day, water molecules move more actively –> more binding to enzymes –> higher rate of photosynthesis
- but too much heat denatures enzymes (lose critical shape) –> water molecules can no longer bind –> cannot photosynthesise –> shrivel up and die
Enzymes are involved in photosynthesis – as light intensity increases, rate of photosynthesis increases until it reaches saturation point (rate cannot increase beyond this point): limiting factor –> graph like enzymes graph
Changes in limiting factors affect the saturation point
What is the relationship between CO2 release and uptake?
use the products from processes of respiration and carbon dioxide, but if photosynthesising at high rate, need to take in more CO2 from environment for enough input
plants take more and more CO2 until light saturation point is reached (maximum rate of photosynthesis)
plants get nitrates from insects they eat to make amino acids (proteins: C,H,O,N), and nitrate, sulfate, phosphate from the soil
creepers need to find a host, prop to climb. when they are young, they grow away from sunlight to find a trunk, and grow horizontally. After touching tree, they grow vertically and develop leaves. At the canopy, the leaves turn from broad and wide to
young plants have tiny roots, less chlorophyll, thinner cells, thinner wax layer, fine xylem tubes, tend to lose a lot of water –> hair on leaf surface to trap moisture –> surface is humid –> prevent excess water loss. different shapes of leaves: palmate, lobed. what factors cause unfolding of leaves? water: hydraulic pressure (pressure travelling from one place to another). undergrowth plant: grow in shade
strategies to absorb maximum sunlight
1. move in direction of light
2. positioning of leaves – grow in mosaic way so they don't overlap, grow in gaps: crown shying
3. some leaves have red undersides to reflect light, upperside very dark green with lots of chloroplasts, spine-like things to increase surface ares
4. whitish small patches act as lenses to focus light to chloroplasts
reduction reaction
light, water and chlorophyll –> ATP + NADPH + O2
light energy converted to chemical energy in the form of ATP (NADPH is the reducing power to cause reduction)
6H2O + 6CO2 –> C6H12O6 + 6O2
H2O –> H+ + e + O
occurs in membrane of thylakoid
epidermis: transparent, no chlorophyll, light can pass through
guard cells embedded within epidermis
mesophyll (inside cells): two layers of cells –> all have chloroplasts, chlorophyll, can absorb light
top layer (rectangular cells): palisade mesophyll. compact, longer axis of palisade mesophyll at right angle to upper epidermis so that more cells are exposed to sunlight. everyone of them has chlorophyll
bottom layer (circular cells): spongy mesophyll
thylakoid
so many membranes increase surface area to volume ratio
chloroplasts have their own nuclei
electrons get excited, shoot out of chlorophyll
leaves have water coming in from the xylem, carbon dioxide from the stoma
chloroplasts made up of many membranes
outer membrane, inner membrane, thylakoid, granum (stack of thylakoids)
membrane of thylakoid made up of phospholipids
proteins: photosystem 1 (PS1): first discovered. P700: best wavelength of light absorbed in reaction centre
photosystem 2 (PS2): discovered later. P680.
Lumen: centre of thylakoid space
enzymes split water molecule
membrane not permeable to hydrogen, hydrogen ions remain in lumen while oxygen is liberated
electron becomes from oxidised state to reduced state (a lot of energy at this stage)
hydrogen ions concentrated, moves out of lumen through carrier proteins, hence producing ATP
NADPH and ATP (in stoma) are the end products, which go on to power the dark reactions
Hydrogen bond
soil water diffuse by osmosis, enters root hairs to enter the xylem in the roots, part of the vascular bundle, travels up stem into leaves
high pressure of water entering stem, xylem (vessel) is like a drinking straw, suction is evaporation through the vessel, transpiration pull, continuous column of water, water also joined to the wall of the vessel
(forces) cohesion + adhesion (water molecule to wall) –> capillary action for transport
because of two factors: continuous column (cut the stem under water so as not to break the column of water to maintain strong suction of water)
aphids suck plant sap
Autotrophic Nutrition – plant cells structure and adaptation
Autotrophs able to synthesise own food – producers
heterotrophs: unable to synthesise own food, get energy from autotrophs – herbivore, omnivore, carnivore
stomata: - makes sugar too, increase osmotic concentration so water can pass through
- takes in air, carbon dioxide used for photosynthesis
- water leaves the cell as water potential is higher inside
- they are on the underside of the leaves to avoid direct sunlight
- guard cells have chloroplasts, can make food, so osmotic concentration/pressure increases and water potential decreases –> water moves into guard cells from epidermal cells which have higher water potential (they do not contain chlorophyll) –> guard cells become turgid; cell wall on the outer side is thinner so stretches more –> hence the guard cells open
- only open when photosynthesising
Plant Pigments
Main pigment: chlorophyll: a, b. absorb blue and red, reflect green
carotenoids: carotene, xanthophyll. absorb blue and green, reflect mostly yellow
phycocyanin: absorb green and yellow, reflect yellow, orange or red
chlorophyll b, carotene and xanthophyll are accessory pigments; chlorophyll a is the main pigment
light comes in a packet: photon – light shines on pigment, vibrates, energy passed on, excite electrons, until energy accumulated in reaction centre, have enough energy to leave orbit, so electron shoots off from reaction centre and is caught by electron transport chain
electron transport chain (ETC): plastoquinons, b6f complex, ferridoxine, plastocyanin
electron from PS2 moves to PS1. as the electron is transported along the ETC, ATP is synthesised. PS2 –> PS1 –> ATP. the lack of 1 electron in PS2 is replaced by the H+ ions from the water sucked up by the plant, H+ ions goes into the lumen.
electron shoots out at both PS2 and PS1
PS2 –e–> PS1 –e–> NADPH
ATP ATP
therefore, product of light reaction is ATP and NADPH
The light reaction involves two sets of pigments: PS2 and PS1. PS2 is responsible for synthesis of ATP and for the photolysis of water into H+ + e + O2-; PS1 synthesises compound NADPH, the reducing power to reduce carbon dioxide to form ATP
The Calvin's Cycle
Light independent reactions (DR)
carbon dioxide + NADPH –> sugar
takes place in the stroma (semi-liquid substance)
RuBP: Ribulose Biphosphate: molecule that will take in carbon dioxide, made up of 5 carbon joined in a row
5 carbon + 1 carbon from CO2 –> 6C –> split into two: 3C (triose phosphate: glycerate). at this stage, take in ATP and NADPH. ATP –> ADP (–> AMP); NADPH <–> NADP+ + H+. One 3C will need 2ATP and 1NADPH to form 3C glyceraldehyde –> product: glucose –> entry of ATP and ADP –> remainder goes back to RuBP: CYCLE
1 of the 3C forms glucose while the other 5 goes back to RuBP
Big picture:
convert solar energy to chemical energy
second step is independent, solar energy already captured, needs carbon dioxide for carbon fixation, using the chemical energy from ATP
destarching: plant kept in darkness for few days
1) put leaf in water – kills the enzymes to stop reaction
2) put leaf in ethanol to decolourise leaf so that colour change can be observed –> ethanol dissolves the lipids in the cell membrane so chlorophyll leaks out
Factors affecting photosynthesis
Carbon dioxide
Light
Temperature: with every 10 degree Celsius increase in temperature, photosynthesis rate doubles
- enzymes: water molecules bind to enzymes to split
- on hot day, water molecules move more actively –> more binding to enzymes –> higher rate of photosynthesis
- but too much heat denatures enzymes (lose critical shape) –> water molecules can no longer bind –> cannot photosynthesise –> shrivel up and die
Enzymes are involved in photosynthesis – as light intensity increases, rate of photosynthesis increases until it reaches saturation point (rate cannot increase beyond this point): limiting factor –> graph like enzymes graph
Changes in limiting factors affect the saturation point
What is the relationship between CO2 release and uptake?
use the products from processes of respiration and carbon dioxide, but if photosynthesising at high rate, need to take in more CO2 from environment for enough input
plants take more and more CO2 until light saturation point is reached (maximum rate of photosynthesis)
plants get nitrates from insects they eat to make amino acids (proteins: C,H,O,N), and nitrate, sulfate, phosphate from the soil
creepers need to find a host, prop to climb. when they are young, they grow away from sunlight to find a trunk, and grow horizontally. After touching tree, they grow vertically and develop leaves. At the canopy, the leaves turn from broad and wide to
young plants have tiny roots, less chlorophyll, thinner cells, thinner wax layer, fine xylem tubes, tend to lose a lot of water –> hair on leaf surface to trap moisture –> surface is humid –> prevent excess water loss. different shapes of leaves: palmate, lobed. what factors cause unfolding of leaves? water: hydraulic pressure (pressure travelling from one place to another). undergrowth plant: grow in shade
strategies to absorb maximum sunlight
1. move in direction of light
2. positioning of leaves – grow in mosaic way so they don't overlap, grow in gaps: crown shying
3. some leaves have red undersides to reflect light, upperside very dark green with lots of chloroplasts, spine-like things to increase surface ares
4. whitish small patches act as lenses to focus light to chloroplasts